Laserfiche WebLink
903808-SS4 CON-41 <br /> 4.3.5.5 Trace Metal Analyses <br /> 4.3.5.5.1 During the 1987 and 1988 WCC sampling rounds, trace metal <br /> analyses were completed for Wells LM 47 through LM 74. The results of <br /> these analyses, which are presented in Table 4.0-7, show that there are no <br /> samples which exceeded the MCL for the metals tested. <br /> 4.3.5.5.2 During the 1986 Radian sampling, however, the onsite Wells <br /> LM 1 through LM 43 were sampled for metals with several exceedances of the <br /> chromium and selenium MCLS. For chromium, 32 of 52 samples collected by <br /> Radian were reported above the MCL of 0.05 mg/1 , with a range of <br /> concentration from <0.005 to 0.41 mg/l . For selenium, 13 of 52 samples <br /> were reported above the MCL of 0.01 mg/l , with a range in concentration <br /> from the detection limit of <0.08 mg/l (above the MCL) to 0.78 mg/l . The <br /> analytical results from the Radian investigation are included in Appendix H. <br /> 4.3.5.5.3 The areal distribution of the chromium and selenium results <br /> above MCL were found to be widespread, and not specifically related to the <br /> six Contaminant Areas. In addition, a comparison of a summary table <br /> provided by Radian of "Analytical Results from Previous Investigations" <br /> (included in Appendix H) contains historical chromium data which are <br /> consistently below the Primary Drinking Water Standards for the onsite <br /> wells listed. Because of the ubiquitous distribution of chromium in almost <br /> all wells sampled by Radian (including those previously considered as <br /> background upgradient wells, LM 12, 0.062 mg/1 ) , the absence of chromium <br /> greater than 0.031 mg/1 in the offsite downgradient wells, and the <br /> discrepancy between historical results and those reported in 1986, the 1986 <br /> Radian results are considered to be suspect and have not been considered to <br /> be indicative of contamination in this report. Similarly, the selenium <br /> values greater than 0.01 mg/l reported by Radian are also distributed <br /> throughout the Depot onsite wells, while all WCC values onsite and offsite <br /> did not exceed 0.007 mg/l . <br /> 4.3.5.5.4 The reason for this apparent anomaly is that the water <br /> samples collected by Radian for metals analysis were not field-filtered <br /> prior to preservation with acid, whereas standard procedures in the Work <br /> 4-185 <br />